The present invention generally relates to air to oil coolers and, more particularly, apparatus and methods for decongealing air to oil coolers.
During cold start or cold operation of engine oil coolers, the oil becomes extremely viscous and the pressure drop through the cooler becomes very high. These coolers are normally fitted with a pressure relief bypass valve which bypasses the cooler if the pressure drop in the cooler becomes excessive. In this case, during cold operation the oil appears congealed in the cooler core, the oil pressure drop is high and oil bypasses the cooler via the bypass valve. This is the normal function and helps to warm the oil up quickly in cold conditions.
The problem is that, under very cold conditions when cold air is flowing over or through the cooler, the oil remains very cold within the cooler core and continues to present a high pressure drop to the bypass valve. With no oil flow through the cooler core, the oil heats up by the heat added in the engine gearbox or generator and may exceed the oil temperature limit before the oil inside the cooler warms up enough to reduce the pressure drop through the core and establish oil flow. This problem is made worse in turbofan engine surface coolers where the oil flow length is distributed over a large arc of the fan case. The pressure relief bypass valve, usually mounted on the cooler, normally provides a source of heat from the warm bypassing oil to warm the core. If the bypass is thermally far away from the oil flow paths within the cooler core, the effect on decongealing will be limited.
As can be seen, there is a need for improved apparatus and methods for decongealing air to oil coolers.